oaf

An oaf is the boring, ill-mannered person you hope doesn't show up at your party and send the other guests running for the door.

There are many ways to be an oaf: you can be loud, insensitive, rude, or just plain stupid. The word is related to the Old English word for "elf," and originally meant a changeling — an elf's child, a little darling not known for good manners — and you probably wouldn't want one of them at your party either.